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Episode 96: Lead Balloon, Surfing with Dynamite

Lead Balloon: A lead balloon cannot fly busted

Surfing with Dynamite: You can use dynamite to make surfable waves busted

Lead Balloon featured the MythBusters at their best: clever design, difficult construction, good results. It was an engineering challenge and Adam and Jamie succeeded with a delicate 10 ft lead cube balloon.

The Surfing with Dynamite continued the trend towards busting Internet videos that has been appearing in MythBusters. In this case, they busted an absurd video that features people throwing dynamite into a canal and catching waves from the resulting churn. It was mostly an excuse to explode 200lbs of TNT beneath the water.

Lead Balloon

Myth: It is impossible to make a balloon out of lead, as in the idiom, "Going down like a lead balloon."

Hot air ballons were invented in 1783 by the Montgolfier brothers in France. The envelope of a modern hot air balloon is quite heavy at 500 lbs, but it is made of light and strong material. Lead sheets, on the other hand, are very heavy and very weak.

Tinfoil experiment

Adam and Jamie each constructed a balloon out of tinfoil. Tinfoil is stronger and 6x lighter and than lead, but this would allow them to test different construction techniques. Adam built his design based on a platonic solid -- the icosahedron -- while Jamie draped triangular pieces over a hemisphere and taped the two halves together. Both designs at their small scale were successful, but that was using tinfoil. Unfortunately for Jamie and Adam, lead foil is "like wet toilet paper" (in Jamie's words).

Small-scale lead balloon test

Jamie and Adam taped together sheets of lead foil on a table, rubbing their facial hair on the tape to get the static out. The design was simple: two sheets of lead foil on top of one another to form a pocket in between. Although tears formed very easily, they were able to inflate their design. It wasn't able to fly as there was too much lead for the amount of helium at that size. By making the balloon larger, they could increase the ratio of helium to lead and make it fly. According to their calculations:

2'x2'x2' design: 225g Helium, 408g Lead, -183g Lift

5'x5'x5' design: 3500g Helium, 2550g Lead, 950g Lift

10'x10'x10' design: 28kg Helium, 10.2kg Lead, 17.8kg Lift

Based on these calculations, they went with the 10'x10'x10' design.

Full-scale lead balloon Test

Adam and Jamie setup shop in an Alameda Naval Base Hanger, where they carefully scrubbed the floor and laid down some paper on top to create their assembly area. Jamie also constructed a swinging boom arm on a forklift so that they could be suspended over the lead sheets as they assembled it.

Adam came up with an origami-like design that would allow them to construct the lead balloon flat and then have it unfurl into a cube as it was inflated, i.e. 'flower-style'. The design appeared to be a sandwich of two square sheets of lead with twelve triangular pieces in between. As the design unfurled, the top and bottom pieces twisted as the triangular pieces sprung up to form the sides. There was much care taken as they assembled the master piece: in addition to the paper and boom arm, they filled the balloon from both the top and the bottom to avoid any pinchpoints that could rip the sheets, and they laid a plastic drop cloth on top to keep the inflation even. They also mixed in air with the helium to prevent the balloon from having too much lift and ripping itself apart -- they knew that they had lift to spare.

True to Adam's design, the 11kg lead balloon twisted and unfurled into a cube. As the balloon gained lift, rips started to appear, but it contiued to fly upwards. Adam hung a little basket with a paper Adam and Jamie from below and they had to hold onto the balloon to keep it from flying upwards.

Adam: "Busted Idiom!"

Their glittery balloon was brought down as Adam and Jamie took turns puncturing it with a baseball. They proceeded to roll it up into a small, 11kg block of lead, illustrating how thin the material really waas.

busted

Surfing with Dynamite

Myth: You can use dynamite to make surfable waves

In an Internet video, some surfers in a city find a canal and drop dynamite in to make some surfable waves:

Can you create a wave with explosives?
Which depth is most effective

Proof of concept experiment + learning to surf

The build team built a water tank in the parking lot and used a dry ice soda bottle bomb as their explosive. This wasn't a small-scale experiment: they just wanted to see what sort of waves and explosion would make and how the varying depths affected it. The set the dry ice bomb off at the bottom, mid-depth, and surface of the tank. The mid-depth seemed to produce the best waves, though the waves didn't break like surf waves.

The build team also went down to Santa Cruz to learn how to surf, which was fun for them though they weren't going to actually surf the explosion themselves. As Dr. Van Romero, VP Research, New Mexico Tech explained, the shockwave from the explosion would be fatal to humans as your lungs would bleed.

Full-scale test

Grant constructed a mechanical paddling robot, aka "Robo-Grant", to surf the waves. Steel arms spun by a motor were mounted on a 10 ft foam surf board. They added foam legs and torso molded off grant as well as a rudder for steering. The paddling mechanism swiveled somewhat like human shoulders and was capable of both freestyle (alternating) and butterfly (simultaneous) strokes.

Grant: "I'm hoping that RoboGrant has been embued with the natural surfing talent that real Grant has"

Kari: "does anybody find it creepy how many "Grant" robots have been on this show? Is it just me or is he trying to clone himself and make a little army?"

They performed their test at a quarry lake at Angels Camp, which was devoid of fish so that no fish would be harmed in the experiment. They found a good spot using a depth finder to set their explosions and did some tests with 50 lbs of TNT to find the right depth. The Internet video only showed about 2-3lbs of dynamite, but expert Frank Doyle figured that they would have to go much bigger. The 50 lbs of TNT at 30ft generated a big explosion, but the wave was only about 1" high. They set off another 50 lb charge at 12 ft and manged a 1 ft high wave, with some tiny breaks at the shore.

Based on these results, they decided to put all their remaining explosions on the line -- 200lbs of TNT. Robo-Grant paddled up to speed going away from the explosion as the TNT was set off 12 ft below the surface. A giant column of water shot up and a wave taller than Robo-Grant sped out, but by the time it reach the robot it seemed to disappear beneath the surface. Unlike the waves you surf on and portrayed in the Internet video, waves from explosions lose energy as they radiate outwards from the explosion. Definitely not surfable.

The TNT experiment was pretty cool, but extremely flawed in design. The one factor that they did not think about was the depth of the water. There is a reason why surfing takes place near shore. In order for waves to incease in amplitude and start breaking the water must start to get shallower. In deep water the wave will have too long a wave form and will not be deep enough. Think of a Tsunami wave. Out in the ocean it is long and not very high, when it gets to shore it increases in high and becomes a problem. Although I agree the video may still be bogus to create that big a wave with three sticks of tnt, I think if they had done the same experiement in shallow water they would created much bigger, surfable waves, and proved it plausible.

I don't think they ignored the water depth. If you look carefully you'll see that they chose an area of the quarry where the water was shallower, and hence the waves were larger here compared to other parts of the lake. It would be very difficult to find a place to do a test with proper shallow water, however, given that the explosion would kill all aquatic life. The fact of the matter is, regardless of water depth, without the constant pressure caused by the ocean swell that keeps real waves going, these shock waves will dissapate with distance - the myth is busted.

Perhaps not one of the better shows but still interesting to watch. In regards to the "surfing" feature, the original questionable footage seemed to have been taken in a canal. The concrete sides and their shape no doubt had some part to play in creating waves. Of course the MB team used a quarry which appeared to be more open (apart from one side) but surely rebound would have played some part.

The Original Wave footage was absolutely fake. I seriously doubt a big company like Quicksilver would want to show footage in which several people are are risking their lives and breaking several international laws. I don't think it was ever intended to be real, the MBs just wanted to see how possible it was.